This invention relates to bundling apparatus and more specifically to a one-piece molded thermoplastic cable tie for forming a plurality of objects into a bundle.
Commercially available one-piece plastic cable ties have excellent performance characteristics when used in moderate to warm temperature environments; however, they have limitations when used in extreme low temperature. This occurs because the strap becomes increasingly brittle with decreasing temperature. Additionally, the presence of teeth on one surface of the strap, as with any discontinuity, has a "notch effect" in that the teeth tend to foster localized stress concentrations at their relatively sharp junctures with the web of the strap when the strap is bent. While such ties can be used at low temperature if handled carefully, severe flexure or shock could result in strap breakage.
Concerning the manufacture of cable ties, one-piece molded theremoplastic cable ties typically include an elongate toothed strap and a locking head joined thereto with one surface of the strap and the head's strap entry face being generally coplanar and with the body of the locking head extending as a cantilever far past the other strap surface. The cavity used for molding the tie is typically formed by a pair of cavity blocks which meet at approximately the longitudinal center line of the strap. When, after completion of molding, the cavity blocks are separated, the tie remains in the block which is in engagement with the head's strap exit face since the head cavity of that block is significantly deeper and has more surface area from which to strip the molded part than the relatively shallow head cavity of the cavity block which engages the strap entry face.
The strap is typically of generally rectangular cross-section and the various walls of the head define a strap-receiving aperture shaped generally complimentary to the strap. It has been found with such a configuration, that two or more knockout pins are normally required to free the tie from the cavity block holding it after the blocks have been opened. The use of several small pins is required because the head's exit face fails to have an impact area sufficiently large to receive the force of a single, larger knockout pin. Using several small pins, while performing satisfactority, greatly increases the complexity of the cavity blocks and several small pins have a shorter service life than a single larger knockout pin.